We live in a digital age, it’s true. Everything is a mouse click or tap away, and while the benefits are enormous, there’s something to be said for going the analog route every once in a while. Take course measurement for example. Just about every runner at this point has, or has had some form of gps tracker with them at a race. They’re wonderful tools to help keep your pace and to keep you aware of your place on the course, but just about every runner using a tracker has discovered that their device doesn’t necessarily match up with mile marks or overall distance. While this may not be too important at a neighborhood run, if you’re going for a PR, or trying to qualify for a certain marathon in New England, the difference can be unsettling which isn’t an emotion you want in the middle of a race!
What’s going on here (usually) isn’t that your device is malfunctioning, or that your course is off. Rather, the definition of a hi-resolution satellite image is one pixel per square meter, and those nodes is what your tracker is finding and moving along, searching for the nearest nodes to your body. This means that while you run a straight line along a road your GPS may be moving in a zig zag, or while you run switchbacks on a trail your tracker may be taking a short cut. As cool as the technology is, it isn’t perfect.
This is where analog comes in! The proper way to measure a course is with a bicycle, following the course the way you would run it (yes, it can be absolutely terrifying). Using a special counter, called a Jones Counter, we count the amount of rotations per mile. We re-calibrate the count several times over the course, to make sure we’re accounting for the gradual deflation of the tire and the change in circumference that that brings. If done correctly, the courses that we measure should be accurate to a 1/4″. Pretty neat, huh?
That said, don’t throw away your Garmin just yet. It’s a fantastic training tool, and provided the course is well measured and marked, you shouldn’t be off by a crazy amount. If you cross the finish line and see a large discrepancy, you should definitely contact the organizers and see if you both can’t work together to find where the error is. The more data everyone has, the better races will be! If you’re curious about the technical specifics of course measurement, this pdf will be an interesting read.
— Tony, Big River Race Management